metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

metrics/writer_test.go

@@ -0,0 +1,22 @@
+package metrics
+
+import (
+	"sort"
+	"testing"
+)
+
+func TestMetricsSorting(t *testing.T) {
+	var namedMetrics = namedMetricSlice{
+		{name: "zzz"},
+		{name: "bbb"},
+		{name: "fff"},
+		{name: "ggg"},
+	}
+
+	sort.Sort(namedMetrics)
+	for i, name := range []string{"bbb", "fff", "ggg", "zzz"} {
+		if namedMetrics[i].name != name {
+			t.Fail()
+		}
+	}
+}